Estimating Sums
34
+23
30
+20
_____
50
38
- 21
40
- 20
_____
20
54
+14
50
+10
_____
60
38
- 32
40
- 30
_____
10
55
+12
60
+10
_____
70
48
- 12
50
- 10
_____
40
21
+23
20
+20
_____
40
53
- 29
50
- 30
_____
20
37
+21
40
+20
_____
60
63
- 42
60
- 40
_____
20
45
+31
50
+30
_____
80
49
- 41
50
- 40
_____
10
56
+31
60
+30
_____
90
35
- 13
40
- 10
_____
30
30
+15
30
+20
_____
50
63
- 41
60
- 40
_____
20